The need to provide secure transactions in the telecommunications industry is well accepted. If service providers are unable to provide a system that supports secure transactions, subscribers will not use wireless devices to make purchases or conduct any other business that must be performed securely. Thus, the telecommunications industry continually tries to provide a secure environment where subscribers may conduct personal and business transactions securely. For example, it is known that the Universal Mobile Telecommunications System (UMTS) standards provide for an authentication key agreement (AKA) and extensible authentication protocol (EAP)-AKA.
In AKA and EAP-AKA a communication device is authenticated using a shared secret key. The shared secret key may reside on a user identity module (UIM) that is part of the communication device. The communication device and a server residing in the network may compute other various keys using the secret key to ensure a secure communication link between the communication device and an access network. This paradigm works well when there is only one UIM.
Subscribers, however, typically have more than one communication device. For example, a subscriber may have a cell phone, a personal digital assistant, a laptop and other communications devices. Each of these devices may receive wireless service through an access network. Also, each one of these devices needs to be authenticated to provide a secure transaction. An efficient way to support a subscriber with multiple communications devices is to give the subscriber a UIM card for each device the subscriber owns, where each UIM card has the same shared secret key. If, however, a subscriber has multiple UIMs, a security hole opens in the AKA and EAP-AKA protocol. If a service provider wants to provide secure communication links and allow a subscriber to have multiple UIM cards with the same shared secret key, the security hole associated with having multiple UIM cards must be addressed.